The general objective of the present invention is to improve the operational efficiency of, and thus save energy in, many industrial, commercial and consumer energy conversion systems which require the introduction of air or other gases in comingling relationship with materials, including liquids, semi-liquids and other flowables. The invention is applicable to both combustion and non-combustion energy consuming processes of a highly diverse nature.
In its essence, the present invention involves a thermodynamic treatment of air or any other gas in a manner whereby the air or gas has dramatically improved ability to initiate and rapidly complete vaporization of liquids at comparatively low temperatures (approximately 130.degree. F. for gasoline), without the addition of external sensible heat: and also has markedly increased ability to promote mixing with other materials due to increased scale of turbulence. Palmer, The Hydrodynamic Stability of Rapidly Evaporating Liquids at Reduced Pressure, Vol. 75, Part 3, JOURNAL OF FLUID MECHANICS, 487-511, 1976, and Bennett and Myers, Momentum, Heat, and Mass Transfer, 2nd Ed., 1974, at 147-151 and 548-550.
The above treatment of air or other gas is very simply obtained by causing a flowing stream of air or gas possessing kinetic energy to impinge on a foraminous barrier and pass through a matrix of dissimilar adjacent nozzle orifices in the barrier to a utilization space beyond the barrier where diverse material processing in energy consuming systems takes place.
Upon impingement at the foraminous barrier, the kinetic energy of the stream is converted to internal energy within the air or gas. After being compressed through the nozzle matrix provided within the barrier, which further increases its internal energy, the pressure of the flowing stream is markedly reduced (Bernoulli's principle). The adiabatic expansion of the air or gas upon leaving the nozzle orifices increases its ability to transfer its unusually high internal energy to another comingling medium in the processing chamber which aids in initiating and completing low temperature vaporization (differential vaporization). Pierce, Microscopic Thermodynamics, 1968, at pages 46-50, 284-285 and 303; Palmer and Maheshri, Enhanced Interfacial Heat Transfer by Differential Vapor Recoil Instabilities, INTERNATIONAL JOURNAL HEAT MASS TRANSFER, 117-122, January, 1981; Anis and Buthod, How Flashing Fluids Change Phase in Pipelines, THE OIL AND GAS JOURNAL, 150-157, June 24, 1974; Hoffman, Differential Vaporization Curves for Complex Mixtures, CHEMICAL ENGINEERING SCIENCE, Vol. 24, 1734-1736, 1969; and Collins, Flow of Fluids Through Porous Materials, 1961, at pages 246-248. Simultaneously, the intensity of turbulence of air or gas exiting the nozzle matrix of the foraminous barrier is drastically increased, without reducing the scale of turbulence, which promotes unusually rapid vaporization, drying or oxidization of another medium in the processing space downstream from the barrier, namely, a liquid, semi-liquid, paste or other flowable; and also enables thorough mixing with such medium, Palmer (supra); Bennett and Myers (supra); and Pope and Goin, High-Speed Wind Tunnel Testing, 99-102, John Wiley and Sons, Inc., New York; and Miyashita et al., Flow Behavior and Augmentation of the Mass Transfer Rate in a Rectangular Duct with a Turbulence Promoter, Vol. 21, No. 4, INTERNATIONAL CHEMICAL ENGINEERING, 646-651, October, 1981.
Typically, the foraminous barrier employed in the thermodynamic treatment of air or gas consists of two screen sections, one relatively coarse and one relatively fine, in a mesh number ratio of approximately 0.375:1. The coarser screen section is placed upstream relative to the air or gas flow path and the finer screen section is placed downstream. The two screen sections are pressed together into firm contact with their interstices and apertures randomly arranged. In situations where it is not desired to promote mixing of the treated air or gas with another medium, the interstices of the two screen sections are arranged symmetrically with the screen apertures in registration. In this case, the mesh number ratio is approximately 0.5:1 to enable proper aperture registration. The mesh number ratio of 0.375:1 where mixing is desired is chosen to assure that the apertures of the two screen sections cannot register when the screen sections are pressed together randomly.
The utilization of two screen sections only in the mesh number ratio specified to promote mixing and rapid, low temperature vaporization, drying or oxidization is critical in the invention and a significant departure from this arrangement will destroy substantially the utility of the foraminous barrier. For example, a single screen of any mesh number will not function properly because, when intensity of turbulence increases as mesh number increases, scale of turbulence decreases inversely. Scale of turbulence is the factor which promotes mixing, whereas intensity of turbulence promotes rapid vaporization. Therefore, when both of these factors are essential to a given process, the dual screen arrangement specified above must be used, Bennett and Myers (supra), and Pruppacher and Rasmussen, A Wind Tunnel Investigation of the Rate of Evaporation, JOURNAL OF THE ATMOSPHERIC SCIENCES, 1257-1258, July, 1979.
The two screen sections which form the foraminous barrier are advantageously formed of stainless steel, but in some cases, can be formed from other materials including other metals and synthetics. The screen sections or the strands from which they are woven may be coated with a catalyst in order to promote the desired chemical effect. In still other cases, the foraminous barrier can consist of two porous membranes of natural or synthetic materials or can be formed by a pair of contacting perforated plates having, respectively, matrixes of relatively coarse and relatively fine square apertures corresponding to the required mesh number ratio stated above, approximately 0.375:1.
It should be stated that significant benefits for the environment are derived from the invention. This is due to the fact that processes carried out at relatively low temperatures produces significantly less pollutants, such as nitrous oxide, compared to processes carried out at higher temperatures.
Examples of other gases, in addition to air, which might be treated in accordance with the invention are carbon dioxide, oxygen and nitrogen.
As suggested previously, thermodynamically conditioned air or gas in accordance with the invention lends itself to a wide variety of uses. One of the most widespread applications of the invention is the spray drying process, where it is believed the invention will constitute a major advance in the art. The scope of application of spray drying and hence the diverse application of the invention is well defined by Masters, Spray Drying, 2nd Ed., 1976, John Wiley & Sons, New York. This publication, and U.S. Pat. No. 4,187,617, describe essentially a one step suspended particle process wherein the feed is a solution, suspension or paste. The resulting dried product conforms to powders, granules or agglomerates. The above-referenced spray drying publication and patent both describe introducing external sensible heat into air before the latter is blown into the drying process chamber. A substantial reduction of such external heat, if not complete elimination of it in some cases, with resultant conservation of energy, is achieved by placing the foraminous barrier in accordance with this invention across the flow path of air or other gas entering the chamber, very slightly upstream from the orifice of the feed nozzle.
The unusually high internal energy of the entering nozzled air, its low pressure, and its high intensity of turbulence developed by passing through the foraminous barrier, combine to effect rapid complete vaporization of the liquid content of the feed, thorough and rapid mixing of the nozzled air with feed particles, or more rapid drying with substantially less energy expended. To achieve these multiple benefits, the temperature of the incoming air or gas need only be 5.degree.-25.degree. F. above the dew point temperature of the particular liquid feed.
Another important application of the invention lies potentially in water desalinization by using the foraminous barrier to upgrade flash vaporization to differential vaporization in one or more stages of the system, Howe, Fundamentals of Water Desalination, 1974, pages 67-72 and 149-154.
Another important application of the invention lies in the field of sewage treatment where the foraminous barrier of the invention can be placed across incoming air streams of such systems.
Other practical applications of the present invention include fluidized bed heat exchangers of the types shown in U.S. Pat. Nos. 4,307,773, 4,272,895 and 4,226,830; material treatment systems of the type shown in U.S. Pat. No. 4,109,394; food roasting systems as disclosed in U.S. Pat. No. 3,964,175: and fluid bed driers for foods and other products, U.S. Pat. No. 3,849,900. Other examples of practical uses of the invention are mentioned hereinafter. Such uses are almost without limit, and it should be understood that the principle of the invention is applicable to any system where it is required or desirable to achieve rapid low temperature vaporization, together with thorough and continuous mixing of a product or product component with air or other gas, without the necessity of applying great amounts of external sensible heat to the air or gas or to the product being processed.
Other features and advantages of the invention will become apparent during the course of the following detailed description.